This invention relates to a color LCD (Liquid Crystal Display) panel, and more particularly to a thin film two-terminal type active matrix color LCD.
The active matrix LCD, in which each pixel unit in an LCD panel is connected in series to a switching element, has rapidly progressed in pixel volume, in response speed, and in high level of contrast. In heretofore disclosed active matrix LCD of trial production, a thin film transistor (TFT) having amorphous Si or poly Si as semiconductor material is used as the switching element.
On the other hand, an active matrix LCD in which thin film two-terminal nonlinear elements (hereafter abbreviated to TFD) are used as the switching elements, is attracting attention from a view of simplification in manufacturing process, high yield rate, and low cost because of its relatively simple structure. This TFD is a nonlinear resistance element.
In these two-terminal element type active matrix LCD (hereafter abbreviated to TFD-LCD), a most promising structure for practical use is an LCD where elements having a metal-insulator-metal structure (hereafter abbreviated to MIM element or MIM) are used. LCD with MIM TFD is hereafter abbreviated to MIM-LCD.
When MIM TFD is connected in series with liquid crystal, the rise time of the changes of "working point of TFD-voltage on liquid crystal-transmission factor of the pixel unit" becomes very sharp because of the strong non-linear character of the voltage to current in TFD.
High speed scanning of the pixel units in LCD can be achieved by this sharp rise time.
MIM-LCD has been disclosed, for example, on "The Optimization of Metal-Insulator-Metal Nonlinear Devices for Use in Multiplexed Liquid Crystal Displays" by D. R. Baraff et al in IEEE Trans. Electron Devices, vol. ED-28 pp 736-739, and on "A Lateral MIM-LCD with 250.times.240 Pixels" by S. Morozumi et al in Technical Reports of Japanese Television Society (IPD83-8), pp39-44, Dec. 1983.
And a MIM TFD with Silicon Nitride of low dielectric constant as MIM nonlinear elements is disclosed on "A New Active Diode Matrix LCD Using Off-Stoichiometric SiN Layer" by M. Suzuki et al in Proceedings of the SID, Vol. 28 pp 101-104, 1987.
And as for a color LCD, there is disclosed on "A 10-in.-Diagonal Full.Color MIM Active Matrix LCD" by H. Aruga et al in Proceedings of the 9th IDRC, pp 168-171, 1989.
In these prior arts, there are provided a lower substrate and an upper substrate. Liquid crystal is sealed between these two substrates.
A matrix of pixel electrodes are formed on the lower substrate and transparent counter electrodes are formed on the upper substrate. A pixel electrode and a part of the transparent counter electrode facing to this pixel electrode constitute a pixel unit with the liquid crystal between these two electrodes.
Data driver X-lines are formed on the lower substrate, and scan driver Y-lines are formed on the upper substrate. At each cross point of the X-lines and the Y-lines, a nonlinear resistance element is formed with one terminal connected to an X-line and the other terminal connected to a pixel electrode.
The counter electrode facing this pixel electrode is connected to a Y-line on the upper substrate.
When a data voltage is impressed on an X-line, and a scanning voltage is impressed on a Y-line, a two terminal element connected to the X-line and the Y-line is activated.
In a color LCD panel, adjacent three pixel units compose a set of RGB pixel units, and RGB data voltages are respectively impressed on RGB pixel units for color display.
In this structure of MIM-LCD, the X-lines on the lower substrate intercept a fairly large amount of the back light.
And therefore, the intensity of the back light must be maintained at a high level, which means a high power consumption.